I have a 2+ year old 50 inch DLP model, and in the last two weeks, at very random times, the volume has shot all the way up to 100 and then freezes. Had to unplug the tv to turn it off, and then plugging it back in seemed to fix things (although I had to do that twice the last time this happened to fix it.) Even when I had the volume down to 0, as I was using my surround speakers, it suddenly shot up to 100.
One other point (may or not be related)
On occasion since I have owned it, the TV would not turn off when I pressed power, but rather would make a screeching noise and turns itself on and off and then stay on. After which, I could just turn it off, so I have basically ignored that problem. Figured I would mention now in case it is connected to the volume thing.